This invention relates to an electrical article, methods for making the electrical article, and circuit articles made therefrom.
The embedded capacitors described in WO 00/45624 include a polymeric insulating or electrically conducting layer between first and second self supporting substrates.
The dielectric material of the insulating layer is typically a metal oxide, such as tantalum oxide, or a high dielectric constant ceramic, such as barium titanate. The dielectric material is typically dispersed in a matrix of some thermally and mechanically stable polymer, such as an epoxy. The epoxy resin may be formulated with about 0.5 to about 8% by weight of a catalyst such as an amine or an imidazole, and 0.5 to 1% of 2,4,6-tris(dimethylaminomethyl)phenol is exemplified. The capacitors can be used as a layer in printed wiring boards and multichip modules to replace surface mounted discrete capacitors.
In one embodiment, the invention is a capacitor including a polymeric dielectric layer, wherein the dielectric layer has a leakage current at 85xc2x0 C. and 85% relative humidity of less than 100 nA/cm2 using a 6 volt bias.
In this invention the polymeric dielectric layer is the reaction product of an epoxy resin and a 9,9-bis(aminophenyl)fluorene curing agent.
In a second embodiment, the capacitor has a change in temperature coefficient of capacitance between room temperature and 125xc2x0 C. of less than 15%.
In a third embodiment, the invention is an electrical article with a dielectric layer including a cured epoxy resin composition, wherein the cured composition includes a unit of Formula 2:
In a fourth embodiment, the invention is an electrical article including a dielectric layer, wherein the dielectric layer is a cured epoxy resin composition, wherein the resin composition includes an epoxy resin and a curing agent of Formula 1:
wherein each R0 is independently selected from H, halogen, linear and branched alkyl groups having 1-6 carbon atoms, phenyl, nitro, acetyl and trimethylsilyl; each R is independently selected from H and linear and branched alkyl groups having 1-6 carbon atoms; and each R1 is independently selected from R, H, phenyl and halogen.
In a fifth embodiment, the invention is an electrical article including a dielectric layer, wherein the dielectric layer includes a cured epoxy resin composition, the composition including an epoxy resin and an aminophenylfluorene curing agent, wherein the composition is heated to the cure temperature at a rate of 1xc2x0 C. per minute.
In a sixth embodiment, the invention is a method for making a capacitor, including providing a first substrate having a major surface; coating an epoxy resin composition onto the major surface of the first substrate, wherein the epoxy resin composition includes an epoxy resin and an aminophenylfluorene curing agent; laminating a major surface of a second substrate to the epoxy resin composition to form a laminate; and heating the laminate for a time and a temperature sufficient to cure the epoxy resin composition.
In a seventh embodiment, the invention is an electrical or electronic device including the capacitor, such as, for example, a circuit board or a flexible circuit.
Compared to epoxy dielectric layers prepared with amine and imidazole catalysts, use of 9,9-bis(aminophenyl)fluorene curing agents reduces water adsorption in the dielectric layer. Furthermore, epoxy layers prepared with the 9,9-bis(aminophenyl)fluorene curing agents are less sensitive to the rate at which the dielectric layer is heated to the cure temperature. This reduced water absorption decreases the change of capacitance with humidity, which decreases the dissipation factor and leakage current in the capacitor structure.
A capacitor having an 9,9-bis(aminophenyl)fluorene cured dielectric layer also has a reduced temperature coefficient of capacitance compared to capacitors having dielectric layers prepared with conventional catalysts. The resulting capacitor structure meets or exceeds X7R capacitor specifications.
The epoxy dielectric layers prepared with the 9,9-bis(aminophenyl)fluorene curing agents are less susceptible to xe2x80x9cpick-offxe2x80x9d when wound into a roll after coating, and are resistant to adhesion loss during the long cure times that are often required as part of multiple epoxy curing steps used during printed circuit board manufacture.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.